1. Field of the Invention
The present invention relates to a method for removal of organic and inorganic materials from a liquid stream by adding a polysaccharide and/or hydrocolloid, optionally, with a subsequent addition of cations to cause gelation of the polysaccharide and/or hydrocolloid.
2. Description of the Prior Art
Significant quantities of discharge water from the oil industry are typically cleaned by separation of oil in cyclones and in flotation plants. These separation processes lower the content of oil hydrocarbons from about 200-1000 mg/l to about 10-40 mg/l. However, most such processes are subject to variations and often do not yield steady discharges below regulatory requirements (generally, requirements are 15-40 mg/l oil in water). Also, these processes are not well suited to handle water-soluble components, such as C1-C5 alkyl phenols that have a considerable influence on the genetics and reproductive ability of marine life.
Today's methods are not optimal for the treatment of the already large and continually increasing volumes of effluent waters that are generated. These methods are also unable to accommodate variations in the extent of contamination of the water. These methods are also dependent to some extent on chemical and mechanical parameters and cannot handle emulsions very well. The above limitations place limits on the degree of water purification that can be achieved, so that water purification requirements and aims of minimizing harmful discharges are not always met.
The industry has continuously been looking for methods and means that can increase the droplet size of materials to improve the cleaning effect of existing equipment. Such means have hitherto included flocculating agents and dosing of extraction means, for example. Both means have limited applications for such wastewaters. Extraction means are not readily available and lead to a different kind of pollution and the flocculating agents give poor results at high temperatures and in large streams of water with variations in chemical parameters. In particular, use of polymers for precipitation does not function satisfactorily as the polymers operate by encapsulation and give particle conglomerates of low strength and a poor tolerance for mechanical stress which may be exerted on such conglomerates in the various separation methods which may be employed, such as cyclones and harsh flotation units.
With regard to oil/water solutions, it is known that alginate transforms these into stable emulsions by associating the oil drops. An application of this is in connection with the production of oil-containing salad dressings.
It is also known that alginate and carrageenan, extracted from brown algae and red algae, respectively, and pectin extracted from fruit are water-soluble biopolymers, and form hydrocolloid solutions in water. The viscosity forming characteristics of these hydrocolloids are determined by the size of the molecules. Alginate is a copolymer of Mannuronate (M) and Guluronate (G) monomers and contains alternating mannuronate blocks, guluronate blocks (MG-blocks), mannuronate blocks (M-blocks) and guluronate blocks (G-blocks), and the gel-forming characteristics of alginate are dictated by the content of guluronate blocks, and also their length. Alginate's ability to form gels arises from divalent cations (for example C++) or other multivalent ions fitting into the G-block structure and thus binding the alginate monomers together to form a continuous network. Application of this mechanism has hitherto been primarily in film-formation, gel-formation in food materials, medicines, textiles, coloured and paper products.
In the field of effluent water cleaning for removal of particulate matter, attempts have been made to use alginate according to the same principle (encapsulation) as with the use of electrolytes, on its own or as a flocculation aid with the use of other flocculating agents, with poor results. It is known from JP 10076274, among others, to use inorganic coagulants, such as Fe3+ with the subsequent addition of water-soluble, large molecular size, carboxylic salts for the encapsulation of coagulated material, and then to add multivalent ions to strengthen the coagulated material.
Furthermore, it is known from JP 58029098 that by dispersing oil and water-soluble alginate in a ratio of about 100 parts oil to 0.5-30 parts alginate, and thereafter adding large amounts of multivalent ions, the oil may be transformed into a solid gel that does not float and can easily be handled for combustion.
It is further known from KR 9609380 that a solution of 0.5-1% alginate in water at a pH 1-4, after mixing in water containing heavy metals at a temperature of 20-40° C., can be used to facilitate filtration of the heavy metals from the water after about 20 to 40 minutes.
It is further known from U.S. Pat. No. 5,520,819 that, by adding and thereafter dissolving alginate and a retardant in a slurry of effluent water, dewatering of sludge can be accomplished. Typically, alginate powder is mixed with carbonates, phosphates or citrates as retardants into a slurry, where multivalent ions are a part of the slurry, so that premature gelling with the metal ions and incomplete agglomeration and coagulation with solid matter in the slurry does not occur. The method involves addition of multivalent ions to react the liquid, particles, retardants and neutralised multivalent ions. Examples show that large amounts of powder are added and the treatment time is several hours. Water and particulate matter can be separated in this manner. The examples also appear to indicate that the water should be subsequently treated with inorganic coagulants.
It is also known from JP 19980827 to dose active carbon powder together with polymer flocculants where the powder is mixed in advance, and where the aim is to make the polymer powder soluble in water with no lump formation. This combination is employed to precipitate solid matter in a batch process over time. According to this patent, the advantage compared to water soluble powder is that the polymer has a longer shelf-life and the carbon powder is a means that makes it easier to dissolve the polymer without the formation of clumps in a liquid when the polymer and carbon are mixed together.